Neutrophil-induced K+ leak in human red cells: a potential mechanism for infection-mediated hemolysis.

Activated neutrophils (AN) when incubated with red blood cells (RBCs) at a ratio of 1:100 were shown to damage RBCs as reflected by an increase in passive potassium (K+) permeability. Oxygenated sickle cells were more susceptible to this injury than normal (AA) RBCs. In both normal and sickle cells, the degree of K+ leak was found to be linearly related to the amount of AN in the incubation mixture. Pretreatment of AA RBCs with low-dose H2O2 resulted in an increased K+ leak after exposure to AN. Compared with patients with stable sickle cell anemia, those who were observed while infected or in crisis had notably more K+ leak from their RBCs after AN exposure. Addition of activated neutrophils from a patient with chronic granulomatous disease resulted in K+ leak from normal RBCs, despite a deficiency in production of toxic oxygen species. Cell-free supernatants from AN also mediated K+ leak. Sickle cells were, again, leakier after exposure to these preparations. Scavengers of toxic oxygen species inhibited up to 40% of the leak, whereas the maximal inhibition obtained by using protease inhibitors was 60%. Addition of autologous plasma in low concentrations inhibited the leak but also resulted in hemolysis, probably via a different mechanism. These studies demonstrate that measurement of passive K+ loss from RBCs allows discrimination between two separate mechanisms of AN-induced damage, an oxidant mechanism, as has been previously described, and a new pathway that appears to be mediated by granule-associated enzymes released from AN. The increased susceptibility of sickle RBCs, especially during periods of increased physiologic stress, suggests that previous membrane damage in vivo may render these RBCs more sensitive to the action of either oxidants or granules released from neutrophils.